TMC428 – Application Note - Trinamic

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TMC428 – Application Note – TMC428 Getting Started – Including StallGuard TM 16 (v. 2.00 / April 14, 2008) 4.6 How to Compare Different Motors Concerning StallGuard Qualification One could directly compare stepper motors concerning the qualification for StallGuard based on the efficiency. The efficiency naturally is not found within stepper motor datasheets. This is because stepper motors are not intend to be most efficient in terms of mechanical efficiency – stepper motors are efficient in terms of pricing, precise control, reliability, torque at low speed, cost concerning mechatronic systems. Comparison by Hand A simple test to compare stepper concerning their efficiency is to short both coils an to turn the axis. A stepper motor of high efficiency breaks stronger than a stepper motor of lower efficiency. Comparison Based on Resonance Frequency Although, the resonance frequency naturally is not found within stepper motor datasheets. This is because the torque almost vanishes at a speed near resonance. It can be avoided by micro stepping or by fast going through the resonance frequency range. Nevertheless, the resonance frequency of a stepper motor can relatively easy be measured and characterizes it concerning its efficiency. A torque proportional to a displacement between rotor and magnetic field forms an harmonic oscillator with a resonance frequency 0 1 2 I J M I , where I = (Ix 2 + Iy 2 ) 1/2 is the absolute value of the coil currents Ix and Iy, and JM is the moment of inertia of rotor axis. This expression can be transformed to 4 2 2 JM 0 I In other words, at a given current I the coupling constant I J M 2 0 I is proportional to the moment of inertia JM times the square of the resonance frequency. This allows comparing stepper motors of different sizes concerning their qualification for StallGuard. "A stepper motor with a high A stepper motor might have higher harmonics. So, the harmonic, the resonance with the highest amplitude. Copyright © 2005-2008 TRINAMIC Motion Control GmbH & Co. KG J is good for StallGuard" Why to Take Both, the Torque and the Moment of Inertia in into Account M 2 0 J has to be on the basis of the first A high torque itself does not imply a high efficiency. Generally, the torque of stepper motors scales with their size and the moment of inertia scales with their size. Competition Based on Torque vs. Speed Diagram If a torque over speed diagram is available for a stepper motor one can compare stepper motors by its efficiency, calculating Nm [rad/s] I [A] 2 * R[ ] + Nm [rad/s] for a given angular velocity. M 2 0
TMC428 – Application Note – TMC428 Getting Started – Including StallGuard TM 17 (v. 2.00 / April 14, 2008) 5. Overview of 'tmc428demo' These routines all together build a simple example application to control the TMC428. One can directly run it together with an TMC428 evaluation kit. Evaluation kits are available via TRINAMIC distributors. These sources are distributed in the hope that they will be useful. They might be a base for your own application. The C code has been compiled using MS Visual C++ 6.0 to build the tmc428demo.exe win32 console application. rs232win.c : routines to access RS232 under win32 (Win9x, NT4, Win2k, XP...) rs232win.h : header file for rs232win.c tmc428spi.c : SPI routine tmc428spi() - calling tmc428spi4win() for the win32 application tmc428spi.h : header file of tmc428spi.c tmc428spi4win.c : routines to access a TMC428 on evaluation board via RS232 under win32 tmc428spi4win.h : header file of tmc428spi4win.c tmc428_base.c : basic TMC428 access routines (basic register IO, ...) using tmc428spi.c tmc428_base.h : header file for tmc428_base.c tmc428_misc.c : Miscellaneous routines (dump of internal TMC428 configuration RAM, calculation of full step frequency from TMC428 parameters, StallGuard demonstration and StallGuard profiler) tmc428_misc.h : header file for tmc428_misc.c tmc428demo.c : MAIN program demo using routines of 'tmc428spi.c', 'tmc428_base.c', ... tmc428demo.exe : Win32 executable - run this program from console (execute: cmd.exe) The LSMD is set to 1 (=2 drivers) for the TMC428 evaluation kit. 6. Overview of 'Sample428_236' This example can be used as a frame for an own micro controller based application. It is written in a compact form. In contrast to the 'tmc428demo' - where a separate routine is available for each type of register – the single routine Send428() is used to handle directly the communication with the TMC428. The SPI datagrams are composed directly – supported by a set of macros. Sample428_236.c : frame for a stand alone micro controller application Sample428_236.h : header file for Sample428_236.c Copyright © 2005-2008 TRINAMIC Motion Control GmbH & Co. KG
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TMC428 – Application Note - Trinamic

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